The present invention relates generally to drive rolls for use in welding-type wire feeders and, more particularly, to a drive roll with an improved engagement configuration.
Certain welding techniques, such as gas metal arc welding (“GMAW”) incorporate a consumable wire electrode. During the welding process, a metal wire is fed through a welding-type gun where the wire ultimately conducts electrical current and serves as a filler metal forming the weld.
A mechanism, commonly known as a wire feeder, is used to advance the wire from a spool to the welding-type gun during the welding process. The wire feeder typically includes two opposing drive rolls. Each drive roll is rotatably mounted such that the wire is fed between the periphery of each complementary rotating drive roll at a pinch zone. The clamping force applied by the drive rolls at the pinch zone may be adjusted; however, a minimum clamping force is required to accurately and reliably advance the wire during operation.
The ultimate force available to advance the wire is generated by a combination of clamping force and the surface contour of the drive roll. One common surface contour consists of a fully-formed, fine pitch knurled surface having a plurality of teeth for engaging the wire (shown in related art FIG. 9). The drive roll teeth engage and compress the wire as the wire is driven through the pinch zone toward the welding-type gun.
The cyclical engagement between the teeth, exacerbated by the stresses imparted by the clamping force, result in drive roll wear. As the drive roll wears, the accuracy of the wire advancement is diminished and can ultimately lead to weak, poor-quality welds or bird-nesting (i.e., the wire becomes tangled in the drive rolls and related mechanisms).
Several techniques have been suggested to increase the useful life of the drive rolls, albeit with limited success. One approach involves selecting a stronger drive roll material and/or performing a surface hardening or other heat treatment of the drive roll to improve its resistance to deformation and wear. While this technique may increase the useful life of a drive roll, the teeth continue to wear and the additional manufacturing operations are costly.
Another approach includes eliminating the teeth found on the drive roll; however, to compensate for the lack of teeth to engage and drive the wire, the clamping force between the drive rolls is increased. This increased force results in greater wear on other components of the wire feeder, such as the drive roller bearings. Additionally, as with the fully knurled design, excessive deformation of the filler wire can result in poor quality welds.
The most prevalent approach implemented to reduce the impact of drive roll wear is to simply include a pair of spaced-apart, fully-formed, knurled grooves on a single drive roll. Thus, when the teeth of the first groove wear out the drive roll is flipped so that the unused teeth of the second groove engage the wire. Once the teeth in the second groove have worn, the entire drive roll is discarded and replaced with a new drive roll.
As a result of the established challenges, the drive roll is seen as a readily consumable part of a wire feeder. Therefore, it would be desirable to have a drive roll capable of providing accurate advancement of the wire over a greater number of cycles, minimizing the stresses imparted to the wire feeder components, maintaining the functionality of the engagement surface, and remaining economical and easy to manufacture.